In electric power steering (EPS) systems some of the highest loads acting upon system components occur whenxe2x80x94due to high handwheel rpm and thus high kinetic energy of the systemxe2x80x94the system is brought to an abrupt halt at an end-of-travel stop. Such uncontrolled stops inflict high impact forces upon electrical and mechanical components causing high stress and possible failure thereof. Thus, it is desirable to control the speed (and thus kinetic energy) of the system components over the extent of their travel and at critical points, such as when the system approaches an end-of-travel stop.
A system for controlling the collisions between elements of an automotive rack and pinion steering apparatus at an end-of-travel stop is disclosed. The system comprises sensors for sensing a set of variables of the rack and pinion steering apparatus, namely an angular position of a steering wheel (or linear position of the rack), a rate of change thereof, and the angle (or linear distance for the rack) to an end-of-stop. From this information, a modification factor n may be calculated that is multiplied by a power steering torque assist command (TAC) to produce a modified torque assist command (MTAC). This modified command may represent a reduced torque assist or even a negative torque assist as required to prevent the steering system from striking the end-of-stop too hard.
In an alternative embodiment, the dynamic data is used to calculate a torque limit to be imposed upon the torque assist command whenever the steering system is close to an end-of-stop. The two embodiments may also be superimposed.
The invention reduces torque at end-of-travel impacts, and helps preserve the mechanical integrity of the power steering system.